This invention relates to antennas and more particularly, to slot antennas adapted for use on aircraft and other high speed vehicles.
Due to the high speed of modern aircraft and missiles, it is important that the size of protuberances from the surfaces of the craft be kept small, or possibly eliminated. As all such craft have electronic equipment which require antennas, considerable work has been done toward reduction of the size of such antennas and mounting such antennas flush with the surface of the craft. Antennas employing a slot radiator are particularly useful for flush mounting as the slot is located flush with the skin of the craft and is backed by a cavity within the craft. These slot antennas comprise a slot from which electromagnetic energy is radiated, a cavity, and a probe for applying energy to the antenna in the cavity. The slot opening itself is usually not an actual opening that will create drag but rather is a sheet of dielectric material flush with the hull. The dimensions of a radiating slot antenna are generally determined by the frequency of the energy to be radiated therefrom. For very high frequencies, the dimensions of a slot become small and, in order to obtain good directivity and gain, it is often necessary to employ an array of these slot antennas. The use of an array of slot aerials also lends itself to beam steering by controlling the phasing of the energy applied to the probe behind each slot.
Small changes in the frequency of energy input to slot antenna with resident cavities produce changes in the impedance of the antenna which restricts the frequency operation of the slot antenna to the design frequency plus or minus approximately a three percent change in frequency. Such a relatively narrow frequency band of operation greatly limits the use of present slot antennas.